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<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> get</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return changes;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public string Issues</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> get</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return issues;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> set</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> issues = value;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> [AttributeUsage(AttributeTargets.Assembly)]</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public class SupportsWhatsNewAttribute : Attribute</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">从上面的描述可以看出，上面的代码非常简单。但要注意，不必将</span><span lang="EN-US">set</span><span style="FONT-FAMILY: 宋体">访问器提供给</span><span lang="EN-US">Changes</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">DateModified</span><span style="FONT-FAMILY: 宋体">属性，因为在构造函数中，这些参数都是必选参数</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">为什么需要</span><span lang="EN-US">get</span><span style="FONT-FAMILY: 宋体">访问器？因为以后需要读取这些特性的值时，就可以使用它们</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<h4 style="FTEL: 21.45pt"><span lang="EN-US">2. VectorClass</span><span style="FONT-FAMILY: 黑体">程序集</span></h4>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">本节就使用这些特性，我们用前面的</span><span lang="EN-US">VectorAsCollection </span><span style="FONT-FAMILY: 宋体">示例的修订版本来说明。注意这里需要引用刚才创建的</span><span lang="EN-US">WhatsNewAttributes</span><span style="FONT-FAMILY: 宋体">库，还需要使用</span><span lang="EN-US">using</span><span style="FONT-FAMILY: 宋体">语句指定相应的命名空间，这样编译器才能识别出这些特性：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">using System;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using Wrox.ProCSharp.WhatsNewAttributes;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using System.Collections;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using System.Text;</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">[assembly: SupportsWhatsNew]</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在这段代码中，添加了一行用</span><span lang="EN-US">SupportsWhatsNew</span><span style="FONT-FAMILY: 宋体">特性标记程序集本身的代码。</span><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面考虑</span><span lang="EN-US">Vector</span><span style="FONT-FAMILY: 宋体">类的代码。我们并不是真的要修改这个类中的任何内容，只是添加两个</span><span lang="EN-US">LastDateModified</span><span style="FONT-FAMILY: 宋体">特性，以标记出本章对</span><span lang="EN-US">Vector</span><span style="FONT-FAMILY: 宋体">类进行的操作。并把</span><span lang="EN-US">Vector</span><span style="FONT-FAMILY: 宋体">定义为一个类，而不是结构，以简化后面显示特性所编写的代码</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">VectorAsCollection</span><span style="FONT-FAMILY: 宋体">示例中，</span><span lang="EN-US">Vector</span><span style="FONT-FAMILY: 宋体">是一个结构，但其枚举是一个类。于是，这个示例的下一个版本在查看程序集时，必须同时考虑类和结构。这会使例子比较复杂</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">namespace Wrox.ProCSharp.VectorClass</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> [LastModified("14 Feb 2002", "IEnumerable interface implemented " +</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> "So Vector can now be treated as a collection")]</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> [LastModified("10 Feb 2002", "IFormattable interface implemented " +</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> "So Vector now responds to format specifiers N and VE")]</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> class Vector : IFormattable, IEnumerable</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public double x, y, z;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public Vector(double x, double y, double z)</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> this.x = x;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> this.y = y;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> this.z = z;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> [LastModified("10 Feb 2002",</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> "Method added in order to provide formatting support")]</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public string ToString(string format, IFormatProvider formatProvider)</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if (format == null)</span></p>
<p class="a6" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> return ToString();</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">再把包含的</span><span lang="EN-US">VectorEnumerator</span><span style="FONT-FAMILY: 宋体">类标记为</span><span lang="EN-US">new</span><span style="FONT-FAMILY: 宋体">：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> [LastModified("14 Feb 2002",</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> "Class created as part of collection support for Vector")]</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> private class VectorEnumerator : IEnumerator</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">上面是这个示例的代码。目前还不能运行它，因为我们只有两个库。在描述了反射的工作情况后，就介绍这个示例的最后一部分，这一部分查找和显示这些特性。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">为了在命令行上编译这段代码，应键入下面的命令：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><strong><span lang="EN-US">csc /target:library /reference:WhatsNewAttributes.dll VectorClass.cs</span></strong></p></div>
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<h1 id="divCurrentNode2" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165366.htm'><font color='red'>10.1.2 定制特性示例WhatsNewAttributes</font></a></h1>
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<div style='float:left;width:49%'>·<a href='100165363.htm'>9.2 小结</a></div><div style='float:right;width:49%'>·<a href='100165364.htm'>10.1 定制特性</a></div><div style='float:left;width:49%'>·<a href='100165365.htm'>10.1.1 编写定制特性</a></div><div style='float:right;width:49%'>·<a href='100165367.htm'>10.2 反射</a></div><div style='float:left;width:49%'>·<a href='100165368.htm'>10.2.1 System.Type类</a></div><div style='float:right;width:49%'>·<a href='100165369.htm'>10.2.2 TypeView示例</a></div></div>
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